import java.util.LinkedList;
import java.util.Queue;

public class Test {
    public static void main(String[] args) {
        //
    }
}

class Solution
{
    int[] dx = {0, 0, 1, -1};
    int[] dy = {1, -1, 0, 0};
    int m, n;
    public void solve(char[][] board)
    {
        m = board.length; n = board[0].length;
        // 1. 先处理边界的 'O' 联通块，全部修改成 '.'
        for(int j = 0; j < n; j++)
        {
            if(board[0][j] == 'O') bfs(board, 0, j);
            if(board[m - 1][j] == 'O') bfs(board, m - 1, j);
        }
        for(int i = 0; i < m; i++)
        {
            if(board[i][0] == 'O') bfs(board, i, 0);
            if(board[i][n - 1] == 'O') bfs(board, i, n - 1);
        }
        // 2. 还原
        for(int i = 0; i < m; i++)
            for(int j = 0; j < n; j++)
                if(board[i][j] == 'O') board[i][j] = 'X';
                else if(board[i][j] == '.') board[i][j] = 'O';
    }
    public void bfs(char[][] board, int i, int j)
    {
        Queue<int[]> q = new LinkedList<>();
        q.add(new int[]{i, j});
        board[i][j] = '.';
        while(!q.isEmpty())
        {
            int[] t = q.poll();
            int a = t[0], b = t[1];
            for(int k = 0; k < 4; k++)
            {
                int x = a + dx[k], y = b + dy[k];
                if(x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O')
                {
                    board[x][y] = '.';
                    q.add(new int[]{x, y});
                }
            }
        }
    }
}

